Development of the multiple organ dysfunction syndrome (MODS) is a common after severe trauma, particularly when patients develop shock, metabolic acidosis, and require multiple transfusions of packed red blood. The development of MODS after hemorrhage and trauma clearly is related to the magnitude of the resulting systemic inflammatory response. Accordingly, investigators have invested a great deal of effort to learn more about various signaling pathways that lead to the activation of the innate immune system and the elaboration of pro-inflammatory mediators after trauma/hemorrhage. Although a great deal remains to be learned, important elements of many of the key signaling pathways already have been elucidated. In contrast, the biochemical and cell biological underpinnings for post-traumatic organ dysfunction per se remain very poorly understood. It is known, however, that the histopathology of MODS in humans is remarkably bland; massive cell death, whether due to necrosis or apoptosis, is almost certainly not the cause of MODS. Rather, the final step in the development of MODS is probably the widespread dysfunction of parenchymal cells in multiple organs as a result of the deleterious effects of a poorly controlled systemic inflammatory response. Thus, a hugely under-explored area of research can be summarized by this question: How does post-traumatic dysregulation of the inflammatory response lead to parenchymal cell dysfunction? Based on our work during the previous cycle of funding of this grant as well as other work performed recently by our research group, we hypothesize that post-traumatic MODS results, at least in part, from perturbations in the expression and subcellular localization of tight junction (TJ) proteins in multiple epithelial tissues, such as those found in the lung, liver and gut. Because it is relatively easier to investigate epithelial TJ function in the intestinal mucosa than it is in other tissues, our efforts will focus on the gut, although key findings will be corroborated by carrying out experiments to study epithelial TJ function in other organs (i.e., the liver and lungs). The work will be organized under these Aims. (1): Test the hypothesis that hemorrhagic shock/resuscitation (HS/R) in mice leads to alterations in TJ structure and function in multiple epithelia via mechanisms that depend on the formation of nitric oxide, reactive oxygen species, and/or peroxynitrite. (2) Test the hypothesis that HS/R-induced derangements in gut, liver and lung epithelial TJ structure and function are mediated, at least, in part by binding of HMGB 1 and/or other related ligands to the receptor for advanced glycation end-products. (3) Test the hypothesis that IL-6 is a key mediator of HS/R-induced derangements in gut, liver and pulmonary epithelial TJ structure and function. (4) Test the hypothesis that timely treatment with nictoninamide adenine dinucleotide (NAD +) can ameliorate HS/R-induced alterations in gut, lung, and liver epithelial dysfunction.